With the continued scaling of semiconductor or micromachined device dimensions, it is increasingly difficult to form metal structures in deep cavities. Specifically, as scaling increases, the aspect ratio of deep cavities increases and successful metallization of deep cavities becomes more difficult.
A conventional technique for metallizing deep cavities uses a shadow mask process whereby a mask of a desired pattern is placed between the deposition source and the target substrate, so that only material that passes through openings in the mask is deposited on the substrate. The shadow mask process requires special tools and fixtures to handle the shadow mask. Therefore, shadow mask processes exhibit low throughput. Further, shadow mask processes utilize an expensive, non-reusable mask. Also, shadow mask processes suffer from poor pattern resolution and misalignment problems. While the shadow mask process is prevalent, it is generally not compatible with a CMOS foundry.
Another technique for metallizing deep cavities includes spray coating whereby a fine mist is deposited to form a mask over a target substrate before a metal is deposited through the spray coated mask. However, spray coating processes are typically expensive and also exhibit low throughput. As a result, this technique is generally limited to research and development facilities and is rarely used in a production environment.
Deep cavity metallization may be useful in the fabrication of a number of semiconductor or micromachined devices, such as for forming micro-electromechanical systems (MEMS) devices. Such devices may include metallized cavity structures, such as floating metal structures that are not connected electrically. However, deep cavity metallization suffers from difficulties as aspect ratio increases.
Accordingly, it is desirable to provide simpler and more efficient CMOS compatible methods for forming metal structures in deep cavities. Also, it is desirable to provide alternative methods for fabricating semiconductor or micromachined devices with metal structures and/or improved methods for forming self-aligned deep cavity metal structures. It is desirable to offer methods that overcome limitations of conventional CMOS foundry compatibility with MEMS process techniques in applications which require patterning of metal in deep trenches, cavities or pad openings. Further, it is desirable to provide methods for fabricating semiconductor or micromachined devices that minimize shadowing effects, pattern distortion and misalignment inherent to conventional processing. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background.